Transcript neuro3

S1
Family Weekend
Dr. Davis in Office or Lab
10-11:30 am
Concerning Test # 1
Types of questions
Recall information
Apply to situations
Chapter questions
Refugee physiology
Check Moodle site for 1QQ grades
28 September Topics
Graded potentials
Action Potentials
Properties of V-gated ion channels
AP conduction
1QQ # 10 for 8:30 class
1. At resting membrane potential
a)
b)
c)
d)
e)
The concentration gradient favors the entry of Na+
The electrostatic driving force favors the entry of Na+
The concentration gradient favors the exit of K+
The electrostatic driving force favors the exit of K+
The membrane is more permeable to Na+ than to K+.
2. Suppose you have a cell with the normal concentrations of
Na+ and K+ on either side of the membrane, and you
were able to make the membrane absolutely and
completely impermeable to Na+.
A) What would the membrane potential be? (include the
units.)
B) What equation would you use to calculate the
membrane potential?
1QQ # 10 for 9:30 class
1. At the equilibrium potential for Na+
a)
b)
c)
d)
e)
The concentration gradient favors the entry of Na+
The electrostatic driving force favors the entry of Na+
The concentration gradient favors the exit of K+
The electrostatic driving force favors the exit of K+
The membrane is more permeable to Na+ than to K+.
2. Suppose you have a cell with the normal concentrations of
Na+ and K+ on either side of the membrane, and you
were able to make the membrane absolutely and
completely impermeable to K+.
A) What would the membrane potential be. (include the
units.)
B) What equation would you use to calculate the
membrane potential?
S1
S2
Excitable membranes & special structures make
Neurons good Electrical Communicators
Ligand-gated ion channels in membranes of
dendrites and soma…. Graded potential
conducted decrementally
}
receiving Axon hillock “integrates” and
produces an “all-or-nothing”
Action Potential conducted nondecrementally and
unidirectionally.
}
Synapse on
other neurons,
skeletal muscle,
smooth muscle,
cardiac muscle,
glands
sending
Voltage-gated ion channels in membrane of axon hillock and axon…..
Action potentials = “all or nothing!”
S3
Types and locations of Ion Channels
Sensory neuron
Leak Channels
Gated Channels
….. Ligand-gated
….. Mechanically-gated
….. Voltage-gated
w/ LGCs and MGCs
Intracellular
Recording
Electrode or
Stimulating
Electrode
Interneurons & Motoneurons
w/ LGCs
w/ VGCs
S4
Expanded on next slide
What happens when the
membrane is
depolarized by more
than about 15 mV?
Action potentials are all or nothing.
Analogy of
shutter release
pressure on a
camera, either
trips shutter or
not.
How is the intensity of a
stimulus encoded by action
potential if all action potentials
have the same size (amplitude)?
S5
Relevance of the GHK equation
S6
To reset from inactivated state
to closed state, membrane must
repolarize.
Open at -55 mV
Membrane must repolarize to
“reset” Na+ Channels to be
capable of opening again.
Compare and contrast voltagegated Na and K channels based on
time to open and duration of
open time.
S7
Voltage-gated Na+ channel
Tetrodotoxin from ovary of
Puffer fish, used in
Japanese sushi (fugu)
scienceblogs.com/.../upload/2006/03/channel.jpg
S8
What types of ion-channels are
labeled in this neuron in red?
TTX with red fluorescent marker
S9
Rising
Phase
Falling
Phase
Relative permeabilities
Duration of AP
Refractory periods
absolute RP
relative RP
Why does the
peak of the
action potential
not reach ENa?
Properties of V-gated
Na+ and K+ channels
account for the shape
of the action potential
and the refractory
periods.
S 10
S 11
Natural ways to Initate an
Action Potential
Graded depolarization in
cell body reach threshold
at axon hillock
Graded depolarization in
in receptive membranes of
sensory neurons reach
threshold for AP. i.e.
nociceptors and stretch
receptors.
Unstable membrane
potential cycles: pacemaker
potentials in pacemaker cells
of heart, smooth muscles of
gut, and medullary neurons
for respiratory rhythm.
S 12
Who
Cares?
Novacaine, lydocaine, xylocaine,
All block voltage-gated Na+ channels
Prevent action potentials, so stimulus
does not result in an action potential
in sensory neurons which would
convey that information to the brain
where person would be conscious of
the stimulus!
S 13
Questions About Action Potential Conduction:
How does an action potential move along the axon?
Why doesn’t the amplitude get smaller with distance?
Why is the conduction of an action potential unidirectional?
What is the absolute refractory period and what is going on with voltage gated sodium
channels that accounts for the absolute refractory period?
What is the relative refractory period and what is going on with voltage gated sodium
channels that accounts for the relative refractory period?
Axon
Hillock
Axon
S 14
In unmyelinated axons, action potential must be generated at each
point along the membrane, a relatively slow process that involves influx
of Na+ which sets up positive feedback cycle.
In myelinated axons, action potential must be generated only at the
nodes of Ranvier, which allows AP to be conducted much faster and
with fewer ions moving, and thus less energetically expensive.